Data Sheet

LJ1269HC
Rev1.0 Page 25 Web: www.ljelect.com
3.4.4. Quadrature Mixer - ADCs – Decimators
The mixer is inserted between output of the RF buffer stage and the input of the analog to digital converter (ADC) of the receiver
section. This block is designed to translate the spectrum of the input RF signal to base-band, and offer both high IIP2 and IIP3
responses.
In the lower bands of operation (290 to 510 MHz), the multi-phase mixing architecture with weighted phases improves the
rejection of the LO harmonics in receiver mode, hence increasing the receiver immunity to out-of-band interferers.
The I and Q digitalization is made by two 5th order continuous-time Sigma-Delta Analog to Digital Converters (ADC). Their gain
is not constant over temperature, but the whole receiver is calibrated before reception, so that this inaccuracy has no impact on
the RSSI precision. The ADC output is one bit per channel. It needs to be decimated and filtered afterwards. This ADC can also
be used for temperature measurement, please refer to section 3.4.17 for more details.
The decimators decrease the sample rate of the incoming signal in order to optimize the area and power consumption of the
following receiver blocks.
3.4.5. Channel Filter
The role of the channel filter is to filter out the noise and interferers outside of the channel. Channel filtering on the LJ1269HC is
implemented with a 16-tap Finite Impulse Response (FIR) filter, providing an outstanding Adjacent Channel Rejection
performance, even for narrowband applications.
Note to respect oversampling rules in the decimation chain of the receiver, the Bit Rate cannot be set at a higher value than 2
times the single-side receiver bandwidth (BitRate < 2 x RxBw)
The single-side channel filter bandwidth RxBw is controlled by the parameters RxBwMant and RxBwExp in RegRxBw:
 W hen FSK modulation is enabled:
 W hen OOK modulation is enabled:
The following channel filter bandwidths are accessible (oscillator is mandated at 32 MHz):
Table 14 Available RxBw Settings
RxBwMant
(binary/value)
RxBwExp
(decimal)
RXBW(kHZ)
FSK
ModulationType=00
Ook
ModulationType=01
10b / 24
7
2.6
1.3
01b / 20
7
3.1
1.6
00b / 16
7
3.9
2.0
10b / 24
6
5.2
2.6
01b / 20
6
6.3
3.1
00b / 16
6
7.8
3.9
10b / 24
5
10.4
5.2
01b / 20
5
12.5
6.3
00b / 16
5
15.6
7.8
10b / 24
4
20.8
10.4
Sub GHz FSK/OOK Transceiver Module DATASHEET
R
X
B
W
=
𝐹𝑋𝑂𝑆𝐶
𝑅
𝑋
𝐵
𝑊
𝑀
𝑎𝑛𝑡
×2
𝑅
𝑋
𝐵
𝑊
𝐸
𝑋𝑃
+2
R
X
B
W =
𝐹𝑋𝑂𝑆𝐶
𝑅
𝑋
𝐵
𝑊
𝑀
𝑎𝑛𝑡
×2
𝑅
𝑋
𝐵
𝑊
𝐸
𝑋𝑃
+3